Anatomical and blue intensity methods to determine wood density converge in contributing to explain different distributions of three palaeotropical pine species

Abstract

Wood density constitutes an integrative trait of water relations and growth. We compared the recently developed blue intensity (BI) method, which has only rarely been applied to tropical conifers, for determining wood density with anatomical analyses in studying the three rarely investigated palaeotropical pine species Pinus kesiya, P. dalatensis and P. krempfii, which co-occur in South-Central Vietnam, but differ in their distribution areas. For species comparisons, we also calculated the hydraulic conductivity of the xylem with the Hagen-Poiseuille equation and the water potential causing 50% loss of hydraulic conductivity () based on the anatomical analyses. We hypothesized (i) that the BI values are correlated with the cell wall fractions, the calculated hydraulic conductivity and the values; and (ii) that the wider occurrence of P. kesiya, which also can grow at drier sites, is reflected by higher wood density, lower hydraulic conductivity, lower (more negative) values and a smaller variation in the wood anatomical features across the years compared to the other two species. In agreement to our hypotheses, the results of the BI and the anatomical method were closely correlated, especially for sapwood, and P. kesiya exhibited features that are related to the growth at drier sites and to a higher tolerance towards drought: higher wood density and cell wall:lumen area ratios of its smaller xylem conduits, lower calculated hydraulic conductivity and more negative values. The BI method is well suitable for determining the wood density in tropical conifers. As a fast and inexpensive method, it may be used for initial screening woody species for their water transport capacity and drought resistance.

Blue is the fashion in Mediterranean pines: New drought signals from tree-ring density in southern Europe

“…The BI values were initially linked to the main cell-wall components, cellulose, hemicellulose and lignin (Björklund et al, 2014;Wilson et al, 2014), but recent findings suggest that they depend on cell-wall dimensions, rather than on the cell-wall composition (Björklund et al, 2021). Moreover, another study on conifer species indicated a close link between BI values and cell-wall and cell-lumen ratio (Ho and Thomas, 2021), indicating the relevance of BI for assessing tree hydraulic characteristics. BI series are currently used for several purposes, such as reconstructions of past hydroclimate variability (Seftigen et al, 2020) and dating of historic timbers (Wilson et al, 2017).…”